A significant use of telephone headsets is in connection with automatic in-bound and out-bound telephone systems. Automatic in-bound telephone systems typically include an Automatic Call Distributor (ACD). The ACD is a call control apparatus used for connecting an incoming call to an operator at a workstation. The ACD utilizes a computer to automatically route telephone calls to workstations (also referred to individually herein as a host telephone workstation, host telephone system, or telephone apparatus) connected to the system. The calls may be routed using a variety of algorithms. For example, calls may be routed in a way that balances the call load equally between the workstations, with each workstation occupied by a telephone operator. An ACD may also simply distribute an incoming call by detecting which communication line to an operator is not in use.
Each workstation is connected to a telephone line by an exchange (also referred to as a local exchange). The exchange comprises a trunk for interfacing with a public or private network and a plurality of line circuits, each used for interfacing with one of the workstations. When an incoming call arrives at the trunk, a central control apparatus notifies the ACD of the incoming call. The ACD then determines which workstation receives the incoming call.
In order for the ACD to know which telephone operators are available to receive calls, each telephone operator is required to log on to the system each time he occupies his workstation, and to log off the system each time he leaves his workstation. The ACD will not route calls to any workstations at which the operator is unavailable, so long as the operator has logged off. If the operator returns to his/her workstation and fails to log on, the ACD will continue to route calls away from the operator's workstation, thereby unnecessarily increasing the workload of other workstations.
Typically, an operator utilizes a telephone headset connected to an amplifier which, in turn, is connected to the workstation. The workstation is connected to the ACD. The amplifier is generally used to amplify signals to or from a telephone headset. An operator leaving his or her work station unplugs the headset amplifier from the telephone workstation. The removal of the amplifier is detected by the telephone workstation which serves to notify the ACD that no operator is present at the telephone workstation.
In one application, the headset amplifier receives the audio signal from the telephone workstation, limits the maximum amplitude of the audio signal to improve operator safety, and provides a power output to drive the speaker of the telephone headset. The headset amplifier may provide power for the headset microphone, receives the audio signal from the microphone, and modifies the gain of the audio signal from the microphone.
In one prior art system discussed in U.S. Pat. No. 5,226,077, an operator may log off automatically by unplugging the headset or amplifier from the workstation. Such a system is illustrated in FIG. 1. A workstation 2, which is normally one of several workstations connected to the telephone system 8, has an amplifier 4 between the telephone system 8 and the headset 20. A cord 6 connects the amplifier 4 to the telephone system 8. The amplifier is powered by the telephone system 8, and draws a current of several milliamps from telephone system 8. The cord 6 includes the conductor 10 for DC power and the conductor 12, which provides the ground connection. The transmit signal from the amplifier 4 is normally superimposed on the conductor 10. Alternatively, an additional conductor (not shown) in the cord 6 may be used for the transmit signal. Finally the cord 6 includes receive conductors, which have been omitted for clarity. The cord 6 is interrupted by the connector 14, comprising the plug 16 and the socket 18. The connector 14 allows the amplifier 4 and the headset 20 to be disconnected from the workstation.
The headset 20 includes an earphone (not shown) and a microphone (not shown). Typically, an electret microphone is used, which requires that the amplifier 4 supply DC power of a few volts at between 15 and several hundred microamps to the headset. A cord 22 interconnects the headset 20 and the amplifier 4. The cord 22 includes the conductor 24 for DC power and the conductor 26, which provides the ground connection. The transmit signal from the microphone iri the headset (not shown) is normally superimposed on the conductor 24. Alternatively, an additional conductor (not shown) may be used for the transmit signal. Finally, the cord 22 includes receive conductors, which have been omitted for clarity. The cord 22 is interrupted by the connector 34, comprising a plug and socket connector (also referred to as a “quick disconnect” or QD). The connector 34 enables the operator to disconnect the headset from the amplifier when he/she leaves the workstation 2. Normally, the connector 34 is mounted in the cord 22 close to the headset, but it can be an integral part of the headset or an integral part of the amplifier.
Applications handling a large volume of telephone calls have a plurality of workstations, each with its own telephone connector 14, amplifier 4, headset 20 and necessary interconnecting cords. The workstations are connected to the telephone system 8. The telephone system may include an Automatic Call Distributor (ACD) for distributing the calls evenly between occupied workstations, i.e., workstations at which an operator is logged on. Alternatively, the ACD may be remote from the telephone system 8.
The telephone system 8 includes an automatic log on/log off system 28 that automatically logs a workstation 2 off the telephone system 8 when the occupant leaves the workstation. Some automatic log on/log off systems automatically log the workstation back onto the telephone system when the occupant returns. Other automatic log on/log off systems require the occupant to log back in manually.
When the amplifier 4 is disconnected from the telephone system 8 using connector 14, the automatic log on/log off system 28 causes the telephone system 8 to take an action that is appropriate in view of the fact that the workstation 2 is no longer occupied. For example, in a small office system with a single telephone operator, it can cause the telephone system to go temporarily into its night service mode so that incoming calls do not go unanswered. In a large system with ACD, it prevents the telephone system from directing calls to the unoccupied workstation. When the amplifier 4 is re-connected to the telephone system 8, the automatic log on/log off system 28 may cause the telephone system to reverse the action previously taken, or the occupant may have to log back in manually.
FIG. 1 shows a telephone system 8 with an automatic log on/log off system controlled by the current sensor 32 that detects whether or not the amplifier 4 is connected to the telephone system by monitoring the current drawn by amplifier 4 from the telephone system 8. Current from a power supply 30 in the telephone system is supplied to the conductor 6, and to the amplifier 4, through the current sensor 32. The current sensor 32 provides an output signal to the automatic log on/log off system 28. When the current supplied to the amplifier is greater than a threshold value, typically about one hundred microamps, the current sensor 32 provides an output signal in a first state that indicates that the amplifier is connected to the telephone system. When the current supplied to the amplifier is less than the threshold value, the current sensor provides an output signal in a second state that indicates that the amplifier has been disconnected from the telephone system. The state of the output signal from the current sensor thus informs the automatic log on/log off system 28 whether or not the amplifier 4 is connected to the telephone system 8, and the automatic log on/log off system can thus cause the telephone system to take appropriate action.
The connector 34 in the cord 22 between the amplifier 4 and the headset 20 enables the occupant to leave the workstation while continuing to wear his/her headset without having to disconnect the amplifier from the telephone system 8. Methods for detecting decoupling of connector 34 are discussed in U.S. Pat. No. 5,226,077. For example, a detector may monitor the current drawn from the amplifier by the headset.
In the prior art, headset amplifiers have used power drawn from the telephone workstations. However, many headset amplifiers in use today have increased power requirements as the amplifier includes a digital signal processor (DSP) for implementing signal processing. Such signal processing may include automatic gain control. The signal processing may serve to protect the user by limiting the maximum volume level output to the user. Due to increased power requirements by the headset amplifiers to implement functions such as gain control, powering the headset amplifier using current drawn from the telephone workstation is often impractical or insufficient. As a result, headset amplifiers are now often powered with a battery or from power derived from the USB port of a PC or from an AC wall outlet using a DC power supply. Batteries provide a convenient power source for a telephone headset amplifier, but, since they have finite life, powering a telephone headset from batteries can be relatively expensive, and can also present reliability problems as power levels decrease.
With the advent of wall outlet, USB Power from a PC or battery powered headset amplifiers, there is a possibility that power to the headset amplifier will be inadvertently lost if the amplifier wall outlet plug becomes dislodged or battery power runs below a threshold level.
Although the prior art systems allow an ACD to automatically detect when an operator has manually disconnected a headset from the headset amplifier or the headset amplifier from a telephone workstation, the prior art systems do not detect when the headset amplifier has lost power. For example, power may be lost when the amplifier mains connector is dislodged or when battery power drops below a pre-determined level. As a result, the ACD will continue to route calls to an operator workstation that has lost power. Furthermore, the operator at the workstation is unaware that power to the amplifier has been lost. An available operator at the workstation will therefore fail to receive calls until power is restored.
The need for an ACD to accurately route calls to available operators is particularly important in the emergency services field. In such an application, the ability of the ACD to detect the availability of an operator and functionality of equipment they use is vital before a call is placed thru to the operator. For example, ACDs are used with abbreviated number systems such as the 9-1-1 system in the United States, which was developed for handling emergency service calls. Similar abbreviated number systems are in place in other countries for handling emergency service calls. Typically, an emergency service call center is connected to the PSTN and routes the emergency calls to an operator at a workstation.
To improve the performance of ACD systems in routing calls to available operators, it is desirable that a telephone workstation detect whether a headset amplifier has lost power. As a result, there is a need for improved methods and apparatuses for headset amplifiers and associated telephone workstations.